A solitary ulcer on the tongue.

Syphilis is a systemic sexually transmitted infection caused by the invasive bacterium Treponema pallidum. The diagnosis remains challenging since the disease is labeled as "the great imitator" due to its broad clinical and histopathological appearances. Due to a significant rise in its incidence rates, syphilis should always be considered as a differential diagnosis of any painless, newly developed, oropharyngeal ulcerated lesion. This case demonstrates the rare clinical appearance of a chancre on the tongue as the primary clinical sign of syphilis.